With the meeting of President Trump and Kim Jong-un of North Korea on Tuesday in Singapore, human rights groups are watching for Mr. Trump to bring up North Korea’s widespread crimes against humanity.

Mr. Kim rules with extreme brutality, making his nation among the worst human rights violators in the world.

In North Korea, these crimes “entail extermination, murder, enslavement, torture, imprisonment, rape, forced abortions and other sexual violence, persecution on political, religious, racial and gender grounds, the forcible transfer of populations, the enforced disappearance of persons and the inhumane act of knowingly causing prolonged starvation,” concluded a 2014 United Nations report that examined North Korea.

Here are some of the atrocities that have happened there.

A network of prison gulags

People accused of political crimes are arrested and sentenced to prison camps without trials, while their families are often kept in the dark about their whereabouts. Up to 120,000 inmates were in the country’s four major political prisons in 2014 and were subjected to gruesome conditions, according to the United Nations report.

Prisoners are starved, forced to work, tortured and raped. Reproductive rights are denied through forced abortions and infanticide. Some are executed — sometimes in public. Hundreds of thousands of political prisoners have died in the camps over the past 50 years, the United Nations report found.

In addition to the political camps, North Korea also operates prisons for those accused of ordinary crimes. Some prisons are short-term labor camps. Others hold prisoners who face long-term torture, starvation and other suffering.

Mr. Kim’s enemies, and family, have been executed

Since Mr. Kim assumed power in 2011, taking over from his father, Kim Jong-il, he has consolidated his power through executions. In the first six years as leader, he has ordered the executions of at least 340 people, according to the Institute for National Security Strategy, a think tank arm of the National Intelligence Service.

In 2016, Kim Yong-jin, the deputy premier for education, was killed in front of a firing squad after showing “disrespectful posture” in a meeting. Hyon Yong-chol, a general over the armed forces, fell asleep in a meeting. He was executed with an antiaircraft gun.

Family is also not off limits. One of Mr. Kim’s uncles, Jang Song-thaek, was convicted of treason. He was then executed with antiaircraft machine guns, and his body incinerated with flamethrowers.

Kim Jong-nam, the estranged brother of the North Korean leader, was killed last year in a very public way: near a check-in counter at Kuala Lumpur International Airport in Malaysia. Two women were seen on security cameras walking up to him and rubbing a substance on his face — a chemical warfare agent known as VX, the United States later determined.

Kim Jong-nam was dead within minutes. The women were arrested, but the United States said evidence showed that North Korea was responsible for the attack.

‘An all-encompassing indoctrination machine’

Often the first human rights violations Westerners ascribe to North Korea, aside from preventing North Koreans from leaving the country, are the lengths it takes to indoctrinate its citizens.

According to the United Nations report, which was prepared by its Commission of Inquiry and is more than 300 pages long, North Korea “operates an all-encompassing indoctrination machine that takes root from childhood to propagate an official personality cult and to manufacture absolute obedience” to Mr. Kim.

Independent thought is bred out and propaganda glorifying the state is plentiful, the report said, as is propaganda intended to “incite nationalistic hatred toward official enemies” like Japan and the United States.

Christianity is deemed a ‘serious threat’

North Korea considers the spread of most religions dangerous, but Christianity is considered a “particularly serious threat” because it “provides a platform for social and political organization and interaction outside the realm of the State,” according to the United Nations report.

Christians are barred from practicing their religion, and those caught doing so are “subject to severe punishments,” the report found. North Korean leaders also conflate Christians with those detained in prison camps, those who try to flee and “others considered to introduce subversive influences,” the report stated.

In interviews with The New York Times in 2012, four North Koreans said that they had been warned that the gulag awaited those who spoke to journalists or Christian missionaries. “If the government finds out I am reading the Bible, I’m dead,” one woman said.

In its 2018 World Watch List, the Christian group Open Doors ranked North Korea the worst nation in the world for Christians, and in a statement last week, the group called on Christians to take part in 24 hours of prayer and fasting on Monday ahead of the meeting between Mr. Trump and Mr. Kim.

‘Deliberate starvation’ as a play for power

Two million to three million people were believed to have died during an extended famine in North Korea in the 1990s, The New York Times reported in 1999, around when the country began to recover.

At the time, North Korea used food as a tool to enforce political loyalty, prioritizing its distribution based on who was most useful to the nation’s political system, the United Nations report stated.

More recently, the inmate population in North Korea’s political prison camps has been culled through “deliberate starvation,” the report found, adding that suspects are also starved “to increase the pressure on them to confess and to incriminate other persons.”

When the 2014 report was conducted, it found that hunger and malnutrition were still widespread problems among the general population, and deaths from starvation continued to be reported.

That prompted the United Nations commission to raise concerns that another mass starvation could occur. “Laws and policies that violate the right to adequate food and freedom from hunger remain in place,” the report said.